‘It knocks your socks off every time, even in your 60s’ … Sebastian Barry, winner of the novel category and favourite for the Costa book of the year.
Photograph: Murdo MacLeod for the Guardian

It is a list of guaranteed to gladden the hearts of anyone who thinks they have left it too late to write their first book. Baby boomers, including Sebastian Barry, Keggie Carew, Francis Spufford and Alice Oswald have swept the board of category winners for the 2016 Costa book awards.

Celebrating books across five categories – novel, first novel, children’s fiction, poetry and biography – the Costa awards pit the winners of each category against each other for the overall book of the year award, to be announced this year on 31 January.

Spufford, 52, who won the first novel award for Golden Hill, a vivid evocation of 18th-century New York described by the judges as a “dazzlingly original tale [heralding] a bold, invigorating new voice in fiction”, said cowardice had kept him from tackling fiction despite his award-winning career in other genres.

“I had the sense of fiction as the form in which you are most likely to expose your inadequacies in human experience and understanding,” he told the Guardian. Joking that publishing a novel in his early 50s was “more selfish than a midlife crisis”, Spufford said older novelists had advantages over younger rivals. “By now, you contain really quite a lot of distilled experience and that is to your advantage over people 20 years younger. But you do have to be able to remember what it was like to be younger than you are now.”

Carew, who has already made her mark as a fine artist, scooped the biography award with her debut Dadland, a memoir-cum-detective story about her father, Tom Carew. She said her late start as a writer was “a case of arrested development”, adding: “It is a debut book, but it is the book for me. I have a shed-full of stuff, but I always knew this was [the one] I was supposed to write.”

Described by the judges as “hilarious and heartbreaking”, Carew’s memoir follows her quest to uncover the truth about Tom as he descends into dementia. A law unto himself, she discovered that the man in whose “gravitational field” she grew up had been a Bulldog Drummond-style action man. Serving as a member of the elite Special Operations Executive, he had worked behind enemy lines in France and Burma during the second world war.

The 59-year-old said Dadland had taken years to write. “I stopped at one point and threw the first draft away. I had a really clear idea of what I wanted to do, but it was like grappling with a wild octopus bringing all the strands together.” Asked what advice she would give others starting out as writers, she advised: “I would say, ‘Don’t do it, it’s hell!’”

Though Carew was the oldest of the first-timers on the list, she was not the oldest overall: Irish novelist Sebastian Barry, now 61, took that accolade, winning novel of the year for Days Without End, about two teenage comrades - one Irish and one American - who get caught up in the civil and “Indian” wars.

The novel, praised in the Guardian as “a work of staggering openness; its startlingly beautiful sentences … so capacious that they are hard to leave behind, its narrative so propulsive that you must move on”, puts Barry in the running for his second overall Costa win.

The Secret Scripture was Costa book of the year in 2008, and even before the category winners were announced, the Dublin-born playwright and novelist was bookies’ 2-1 favourite to take the overall prize for 2016 at the end of the month.

“It knocks your socks off every time, even in your 60s,” he said when it was shortlisted in November. “Winning the Costa changed my life. I was able to send my kids to university with that prize. To be at the cadet stage again, that is so exciting.”

Children’s book winner Brian Conaghan, who won with The Bombs That Brought Us Together, offers hope to unpublished writers with piles of rejection slips from literary agents and publishers, having received more than 200 refusals for his debut The Boy Who Made it Rain, which was published in 2011. His next book, When Mr Dog Bites, was shortlisted for the Carnegie medal.

Years as a frustrated unpublished writer had strengthened him, Conaghan told the Scottish Book Trust last year. “I spent years getting rejection after rejection - basically being told my work was rank rotten – so I’m pretty immune to reviews good or bad,” he said. His latest book was described by Costa judges as “a necessary take on modern life in extraordinary circumstances”.

Alice Oswald, 50, completed the five category winners, taking the poetry award with her seventh collection, Falling Awake. It explores life’s losing struggle with the gravity of nature and is designed to be read aloud. “She finds words for encounters with nature that ordinarily defy language,” wrote Observer reviewer Kate Kellaway.

All five writers receive £5,000 and are now in the running for the Costa book of the year, worth £30,000 and announced on 31 January.

• This article was amended on 2 February 2017. An earlier version conflated details of Brian Conaghan’s first and second books.